1. Field of the Invention
The present invention relates to a retractable zoom lens having a variable aperture-stop mechanism for varying a full-aperture F-number in accordance with the focal length of the zoom lens.
2. Description of the Related Art
In zoom lenses (zoom lens barrels) for compact cameras which include a lens shutter, specifically in such zoom lenses with a high zoom ratio, the maximum aperture size is varied in accordance with variations in the focal length of the zoom lens since harmful rays of light need to be shut out at the wide-angle extremity and the full-aperture F-number (full-aperture F value) needs to be reduced at the telephoto extremity.
Variable aperture-stop mechanisms for making the aperture size adjustable are generally thick (large in size) in the optical axis direction, which is conventionally an obstacle to reduction in length of a retractable type of lens in its fully retracted state (accommodated state). In addition, although a multi-function diaphragm control mechanism that is a combination of a shutter and a variable aperture stop is known in the art, both the mechanical structure and the electrical control system of such a multi-function diaphragm control mechanism are complicated because each of the shutter and the variable aperture stop needs to be controlled with precision. Accordingly, it is costly to adopt such a multi-function diaphragm control mechanism.